There are several possibilities but without knowing exactly how the new kitchen will look it is difficult to suggest the best one. One option might be to offset the line horizontally below the cut off height until you reach a vertical wall, and then either make a new vent connection or offset back to the original one above the ceiling.

: I have a "U" shaped kitchen that my wife wants to update/change. One of the changes invovles cutting one wall (non-load bearing) down to counter height so she can look into the famaily room from the kitchen.

: One problem - the vent stack for the sink currently passes up through this wall.

: If I chop the wall in half - where does the vent stack go? The sink sits 5' from the nearest vertical full height wall - do I just run a horizontal vent pipe throught he back of the base cabinets to the other wall...or treat the sink like an island and do the "up and over" vent design before I run to the vertical wall.